This invention relates to apparatus and methods for controlled delivery of purified cryogenic liquid, such as liquid nitrogen.
In various applications, it is important to deliver a metered amount of cryogenic liquid. For example, thin-wall containers, such as plastic, aluminum or steel beverage cans, can be used to contain non-carbonated beverages by adding a metered amount of inert cryogenic liquid immediately before capping the can. When vaporized, the inert cryogen increases internal can pressure which strengthens it, helping the can resist collapse, for example, when stacked for storage or for transport.
Controlled delivery is important in such applications. Too little cryogen will not provide adequate pressure (strength), and the can may fail to withstand forces encountered in stacking and shipping. Too much cryogen can create excessive internal can pressure, deforming the can and possibly exploding it. Commonly owned U.S. Pat. No. 4,715,187 discloses apparatus for controlled delivery of liquid cryogen.
In some applications, the cryogenic liquid must be extremely pure, and it is important to remove impurities found in standard large scale sources of cryogen. Some applications, e.g., where the cryogen is mixed with a food or beverage that can support microbial growth, require sterile liquid cryogen. In that case, the purification involves removing microorganisms. Filtration is one useful way to purify and/or sterilize cryogen.
Medical uses of cryogenic liquids may also require filtering or sterilization. For example, oxygen used by hospitals is often transported and stored as a cryogenic liquid to reduce storage space requirements. The liquid is vaporized when sterile gaseous oxygen is needed.
Other applications requiring filtered cryogenic liquids include uses involving semiconductor chip fabrication. Such processes require extreme cleanliness.
Brodbeck U.S. Pat. No. 4,620,962 discloses apparatus for sterilizing vaporized liquid cryogen. Segura U.S. Pat. No. 4,759,848 discloses sterilization of cryogen by filtration.
Sterile delivery systems are required for the delivery of cryogenic liquids to aseptically packaged products, e.g., products packaged in an aseptic food packaging assembly line. When such delivery systems are shutdown and flow through the sterilized delivery system is interrupted, microbial contaminants may get into the sterilization system.